On a problem connected with convexity of a derivative

On Sahoo—Riedel equations on a real interval

“…With the aid of Theorem 1 we deduce the following This fact played a crucial role in J. Walorski's paper [6], but the author was assuming there that α > 0 and f is a C ∞ -function.…”

“…The authors dealt with the Stamate type equation and gave the solutions of equations (A) and (B) with k = 0. In the paper On some problem connected with convexity of a derivative J. Walorski [6] solving a problem of M. Merkle (see [4]), was looking for a solution of the following functional equation…”